NLP: What is expected from the output of a perfect coreference system?
The clusters you mentioned at the beginning seem right. A &quot;perfect&quot; coreference system should be able to find all words/phrases that refer to the same object.
However, in language, there will always be some ambiguity. For example, consider the sentences &quot;Bob and John like building. He has fun doing it.&quot;. It is ambiguous whether &quot;He&quot; refers to &quot;Bob&quot; or &quot;John&quot;. In that sense, a perfect coreference system may not even exist theoretically. If it did, it would either avoid classifying &quot;He&quot; or recognize that it could go with either &quot;Bob&quot; or &quot;John&quot;.